Heretofore, this kind of a flexible robot arm has been known as disclosed in Japanese Patent Publication No. Sho 59-21756 (U.S. Pat. No. 4,393,728).
The prior art flexible robot arm disclosed in the publication is provided with a plurality of disc-shaped elements each of which both the top and the bottom surfaces thereof having arched opposed double-curve are formed as contact surfaces, respectively, and at a peripheral portion of each disc-shaped element, a plurality of actuating devices (for example, four devices) each comprising a length of cable, etc., are allowed to penetrate the element at plural spots (for example, four spots) spaced apart from one another at an equal distance in the peripheral direction of the disc-shaped element. Respective leading ends of the actuating devices are independently connected to an element arranged at the most distal end, while respective base ends of the actuating devices are connected to a plurality of drive units (for example, four unit) mounted independently of one another. Each of the drive units serves as selectively drawing or loosening the actuating device interrelating to each other. Such as, for example, a drum unit allowed to bidirectionally rotate by means of a motor, a hydraulic cylinder unit allowed to extrude and retract, etc. are preferably used.
Such a prior art flexible robot arm as described above is adapted to be constructed so as to bend or move in a direction such that at least one of the actuating device is drawn.
Further, as is clearly understood from the foregoing description, in the aforesaid prior art flexible robot arm, the actuating devices are respectively actuated by the drive units mounted independently of one another. Accordingly, when a moving stroke of each actuating device is defined as L, the maximum extruding or retracting length is required at more than 2L in case, for example, of the hydraulic cylinder unit as a drive unit. Therefore, a drive unit section of the flexible robot arm where the same numbers of hydraulic cylinder units as those of actuating devices are mounted thereat requires a large space and hence becomes a remarkably heavy weight. In particular, in order to deal with works to be performed at an area where is further away and extends in wider range, there is provided such a flexible robot arm as connecting a plurality of flexible arms in a series through their respective drive units. In this flexible robot arm, the durability of itself remarkably deteriorate because of a heavy weight of each of the drive units which are respectively connected between the respective flexible arms adjacent to each other.
Further, since a space occupied by the drive section becomes large as mentioned above, the flexible robot arm must be formed in a big size. As a result, it has a further disadvantage such that the work site where the big sized flexible robot arm is used must be limited.